1. Field of the Invention
This invention relates to address translation apparatus for computer systems and, more particularly, to bi-directional address translation apparatus for translating real storage addresses into virtual storage addresses and virtual storage addresses into real storage addresses.
The invention finds particular utility in a computer system structured with virtual storage where commands to the I/O devices are issued with virtual storage addresses.
2. Description of The Prior Art
In the past it has been the practice to have the I/O device control mechanism provide the virtual address to be resolved. This required that for each I/O address register a companion virtual address register had to be maintained and incremented/decremented in synchronization with the I/O address register. The need for having two registers for each I/O address is eliminated by the present invention. A single register can be used because a real storage address can be translated to a virtual storage address which is then incremented and the incremented virtual storage address can be translated to a real storage address. This capability is facilitated by having the entries in the page directory ordered by real addresses rather than virtual addresses.